Intermediate-system-to-intermediate-system (IS-IS) protocol, also known as Dual IS-IS, is a member of the open systems interconnection (OSI) suite of protocols and is a collection of extensions to the base IS-IS protocol Integrated IS-IS was developed to allow routers to support both IP and OSI traffic in parallel.
One feature of IS-IS and Integrated IS-IS routed networks is that they do not require unique internet protocol addresses for each network node. Such OSI communications networks are increasingly integral with or connected to internet protocol communications networks such as the internet. However, because nodes in such OSI networks do not have IP addresses it is not possible to use internet protocol type methods to contact those nodes and carry out management or other tasks remotely over the communications network.
For example, consider a node such as an optical multiplexer in an optical communications network where the optical multiplexer incorporates a router and Integrated IS-IS routing protocol is used. When the new optical multiplexer and router are first installed in the communications network the router needs to be configured correctly in order to operate as required in the particular network environment it is placed in. (Also, if the OSI communications network is to route internet protocol (IP) packets, the router typically needs one IP address for each of its interfaces in order to function appropriately. At present, allocation of the required IP address is done by an operator who travels to the router site, makes a physical connection directly to the router using a text terminal, and manually allocates appropriate IP addresses to the router interfaces. This is obviously time consuming and expensive. It is not possible to remotely connect to the router over the network using internet protocol means because the router interfaces have no IP addresses by which they can be identified. This makes it very hard to remotely manage the router or other network node.
Known methods of automatically allocating IP addresses involve for example Dynamic Host Configuration Protocol (DHCP) or Bootstrap Protocol (BOOTP). However, both these methods are applicable to TCP/IP networks and are not best suited to communications networks which comprise a plurality of directly connected routers or other intermediate systems.
Bootstrap Protocol is defined in the Internet Engineering Task Force's (IETF's) request for comments (RFC) number 951. It is a protocol which enables a network user on a TCP/IP network to automatically receive an IP address and an operating system boot. A BOOTP server, managed by a network administrator, allocates the IP address automatically from a list of available addresses. However, the BOOTP method requires that for a new device to be added to a network and automatically assigned an IP address, it must be added so that it is directly connected to a BOOTP server. This is problematic for complex networks such as those which comprise a plurality of directly connected routers or other intermediate systems. In such cases, new network elements may need to be added so that they are indirectly connected to the BOOTP server. However, this is not possible without using a BOOTP relay server that is directly connected to the new network element. In order to provide an IP address to such a new network element, the BOOTP relay server is used, in addition to the BOOTP server itself. The BOOTP relay is connected directly to the new network element. This is obviously complex and requires BOOTP relay servers to be provided in addition to the BOOTP server.
BOOTP is the basis for DHCP which is a more advanced network management protocol. DHCP can be used to automatically assign IP addresses to hosts (e.g. personal computers, print servers, terminals, etc.) on a TCP/IP network. DHCP is described in IETF RFC 2131. However, DHCP suffers from the same drawbacks as BOOTP with respect to the need for new hosts to be directly connected to DHCP servers.